I need help with replacing values in formulae with links.

I inherited supporting several Excel workbooks with very involved formulae
involving links

For example:
=SUM(IF('\\ttemail\global\Operations\Forecasting\I nbound\[Inbound CC Stats
Call
Volumes.xls]C-Rcvd'!$F$4:$F$978=$B1,'\\ttemail\global\Operations \Forecasting\Inbound\[Inbound
CC Stats Call
Volumes.xls]C-Rcvd'!O$4:P$978,))+SUM(IF('\\ttemail\global\Operat ions\Forecasting\Inbound\[Inbound
CC Stats Call Volumes
Tucson.xls]C-Rcvd'!$F$4:$F$978=$B1,'\\ttemail\global\Operations \Forecasting\Inbound\[Inbound CC Stats Call Volumes Tucson.xls]C-Rcvd'!O$4:P$978))

and what I need to do is a global replace of all the instances of $978 with
$1343

The problem is that when I try to use Edit|Replace (Look in Formulas) the
process seems to get hung.

I assume that each time Excel changes the formula it then tries to update
the cells, and that it would therefore take much longer than necessary.

I even tried using C# and the Excel COM objects to do this programmatically,
but the same problem happened.

How can I accomplish this?
Is there a way to turn off updates as the replacements are being made?